Split-phase induction motor



Jan. 4, 1949. E. M. SMITH SPLIT-PHASE INDUCTION MOTOR Filed Sept. 29, 1944 IN VENT? E0601? '7. 5/7117! A! HTTZMWEY Patented Jan. "4, 1949 attain smr-rnasa INDUCTION Moron Edgar M. Smith, Trenton, n. 1., aasignor to The Minneapolirilonemll Regulator Company,

Minneapolis, Minn, a corporation of Delaware Application September 29, 19, Serial No. 858,!

4 Claims. (01. Ill-I20) The present invention relates to induction motors and more specifically to capacitor run motors operating irom a single phase source oi E. M. F. and to improvements in the arrangements or electrical parts to provide maximum emciency and torque while maintaining economy of construction, facility of assembly, and simplicity oi production line methods.

Such motors employ a capacitor to eiiect substantially a ninety degree shift in one twosets oi operating field windings to operate eiiectively as a, two-phase motor. It is well known that it two or more periodically changing magnetic fields are used to produce a revolving iield for the operation of a motor induction type, the optimum condition is one that will produce a revolving fleld of constant velocity and amplitude through the full 360 degrees oi rotation. In standard multiphase motors this problem does not present any real diiilculties oi solution, but in induction or synchronous types of motors, such as a condenser type motor, which operate as a two-phase motor from a single phase source, the necessary shitting of the line phase creates conditions of undesirable amplitude or phase consideration, from which tact a compromise is usually selected in order to avoid expensive construction, or optlmum production design is sacrificed to provide maximum torque, synchronism pull-out, and so forth. Many schemes to eiiect an arrangement of this sort, 1. e., the operation 01' a two phase motor from a single phase source, have been provided, but it is believed that the arrangement comprising my invention accomplishes this in a novel maner and holds certain advantages to methods known in the art.

In the present invention, the conditions producing an ideal revolving field are controlled by means which afford uniformity to production methods by providing similar physical characteristics for all of the duplicated elements, thereby enabling inexpensive construction 01 the type of motor involved, at the same time providing a motor or maximum torque and emciency.

It is an object oi. my invention to provide an improved motor oi the capacitor run type in which the stator comprises a plurality oiwindings oi an equal number oi turns andequal resistance and which is compact and oi inexpensive construction by virtue oi duplication oi parts.

Further objects of my invention will become preferred type of motor construction, and

Figure 4 is a schematic drawing 0! my motor showing the manner in which the electrical elements thereoi are connected together.

Referring to the accompanying drawings, Figures l, 2, and 3 show the structure 0! a motor oi preferred design incorporating the invention (the selected motor as tar as its physical construction is concerned corresponding to the patent oi Walter E. Edeiman, No. 2,412,254). In these figures, the reierehce numeral II is employed to indicate a rotor of conventional squirrel cage construction. The rotor'ls associated with a stator comprising a plurality oi interlocked stator sections Ii. Each stator section II comprises a plurality oi laminetions ii assembled in stacked relation and is provided with a pole portion ii, a tongue portion I8 and a pair oi lip portions ii and it. The tongue portion ll oi any one stator section ii is adapted to iit between the lip portions it and iI to maintain each stator section in a desired position relative to its adjacent stator sections. The various stator sections are held together radially by the inside suriace ll oi the motor casing II and transversely by means oi a heel portion (not shown) at one end which remains aiter machining surface it to a predemined depth, and a retainer ring it at the ot or end which fits into a grove it. the depth oi which is shownby invisible line I. In the particular embodiment shown in Figs. 1 to 3, there are eight such stator sections. Surrounding the pole portion ii of each stator section [I is a winding generally conical in i'orm. These windings are designated in the drawings by reierence numerals IT to 2!.

It will become readily apparent from the structural arrangements of Figures 1 to 3 thl'it it is highly desirable that the windings I! to It be of uniiorm dimensions. If, however. the same number of equal resistance windings are connected in series in both the capacitor phase and line phase, the voltage drop per winding across the windings oi the capacitor phase will be much higher than the voltage drop per winding across the windings oi theiline phase. This condition of unequal voltage drop per winding is a common dii'iiculty encountered when employing a capacitive reactance to provide substantially a degree shift in phase in one of the sets oi windings relative to the other set oi windings and is due to the fact that the optimum choice oi capacitance to provide this phase shiit usually oflers suiiicient capacitive reactance in series with the capacitor phase windings to bring the circuit to. or substantially near to, resonance and thereby create relatively high voltages across the inductive and capacitive components of the capacitor phase. As a result, it has been su gested in the past to employ a diilerent number of turns or diflerent resistance in the capacitor phase windings than in the line phase windings as a compromise to eilect optimum conditions phase and voltage. This obviously leads to non-uniiormlty in the parts and complicates the assembly oi the motor.

Referring to Figure 4, I have shown schematically the arrangement of my motor in the manner in which various windings are so interconnected to permit the use of identical windings throughout. In this figure. the reference numerals correspond to those previously employed in connection with Figures 1 to 8. The capacitor is designated by the reference numeral 21. The dotted line 28 is employed to enclose the elements of the motor proper, as distinguished from the capacitor associated with the motor. Power is supplied to the motor by line wires 30 and Ii leading to any suitable source of power (not shown) The windings 2i and I9 are connected directly across line wires 30 and 3| in a circuit as follows: from line wire 30 through conductors 32 and i3, winding 2i, conductor 34, winding i8, and conductors 35, I6, and 31 back to line wire iii, The windings i1 and 23 are connected in parallel with windings 2| and I8 across the line wires ill and II by conductors 38. 39, and ii.

Referring now to the capacitor phase, the windings 20, I8, II, and 22 are connected in series with capacitor 21 in a circuit as follows: from line wire 30 through conductors 32 and H, capacitor 21, conductor 45, winding 2:1, conductor 46, winding ll, conductor l1, winding 24, conductcr ll, winding 22, and conductors i9 and 31, back to line wire 3i.

It will be noted from the above that there are iour windings in series between the line wires 3i and II in the capacitor phase. In the main or line phase, on the other hand, there are four windings but there are only two windings which are in series with each other between the line wires. Thus, half of the voltage across line wires 30 and ii is impressed across each of the four windings of the line or main phase. In the capacitor phase, on the other hand, ii. it were not for the capacitor 21, only one-fourth of the line voltage would-be impressed across each of the windings 20, I8. 24, and 22. As explained above, however, the presence of capacitor 21 results in the voltage across the series connected windings 20, 18, II, and 22 being very much higher than that across line wires Iii and ii. The relative voltage drop across the windings in the capacitor phase and that between the line wires is dependout upon the circuit constants oi the motor, such as the value of the combined inductance of windings II, III, 22 and M, the value or capacitor 21 and the "Q of the windings. In the particular arrangement shown in Figure 4, these constants are so selected that the voltage drop across the series connected windings in the capacitor phase is approximately twice the line voltage. It is apparent that, in order for the voltage across the capacitor phase windings to assume a greater value than the line voltage, the. "Q." or ratio of reactance to resistance as the capacitor phase:

loss are identical throughout. As a result, the voltage drop across each oi the windings 20, I8. 24, and 22 is equal to exactly one-half of the line voltage, As previously noted this is the voltage drop which occurs across individual windings of the main phase. Thus, the voltage drop across each oi the windings ot the motor is the same despite the presence or capacitor 21. The windings can accordingly each have exactly the same number of turns and the some resistance and yet result in an arrangement in which the voltage drop per turn is subtantially equal throughout the motor. This, as previously noted, is desirable if the field is to approach a circular revolvin field.

It will be seen from the above discussion that with my arrangement, it is possible to employ windings which are uniiorm throughout, both as to the number of turns and their resistance, regardless oi. whether the windings are in the capacitor or main phases, Furthermore, in spite of using windings of a uniform number of turns, I obtain a motor in which thevoltage drop per turn is uniform throu hout the field structure.

While I have shown in Figure 4 a special case in which the voltage across the capacitor winding is twice that of the line voltage, it is to be understood that the circuit constants may be so selected that the voltage across the capacitor windings is some other multiple of the line voltage. In such a case, the windings of the main phase can be readily re-connected in series-parallel and still provide a uniform voltage drop across each of the windings of the main and capacitor phases. In eneral, it is to be understood that my invention is not to be restricted to the embodiments shown but rather as provided by the appended claims.

I claim as my invention:

1. A split phase induction motor, comprising in combination, a rotor and a stator, a plurality of windings each having an equal number of turns and equal resistance in which the ratio oi the inductive reactance to resistance is greater than unity, a first and second group of said windings being electrically displaced from one another on said stator to provide a flux field therein when energized, said first group or said windings being permanently connected in parallel, and said second group oi said windings being permanently connected in series with each other and with a capacitor to provide a condition of resonance within said second group of windings and said capacitor causing a substantially equal voltage drop per winding and a nearly circular flux field within said stator.

2. A split phase induction motor comprising, a rotor. a stator, said stator including a first group or windings electrically displaced from a second group oi windings to provide a rotating flux field within said stator when energized, each oi said windings having an equal number of turns and equal resistance within the inductive reactance to resistance ratio ior said windings greater than unity, said first group of windings being permanently connected in seriesparallel, and'said second group or windings being permanently connected in series witheach other and with a capacitor to provide a condition of resonance therein causing a substantially equal voltage drop across each oi said windings of both roups and substantial circularity or said flux field within said stator.

3. A split phase induction motor or the capacitor type having in combination, a rotor, a capacitor, a stator comprising a plurality of line phase windings and capacitor phase windings each of which has an equal number of turns and an equal resistance with an inductive reactance to resistance ratio greater than unity, said windings oi said capacitor and line phases being electricaliy displaced from one another, said line phase windings being permanently connected in seriesparallel, and said capacitor phase windings being permanently connected in series with one another and with said capacitor the optimum value of which provides a condition 01 resonance within said capacitor phase and a substantially equal voltage drop per winding.

4. An induction motor operating from a single phase source, comprising, a rotona stator, said stator having a first group ,of windings electrisally displaced from a second group oi windings, each of said windings having an equal number go masses REFERENCES CITED The following references are or record in the file of this patent:

UNITED STATES PA'I'EN'I S Number Name Date 808,303 Palmer Dec. 26, 1905 1,780,881 Kennedy Nov. 4, 1930 Myers Nov. 8, 1932 

